Articles with erosion-resistant surfaces



United States Patent 3,083,448 ARTICLES WITH EROSION-RESISTANT SURFACES Donald Charles Moore and Edwin Albert Taylor, Birmingham, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Dec. 8, 1958, Ser. No. 778,604 Claims priority, application Great Britain Dec. 11, 1957 4 Claims. (Cl. 29-198) This invention is concerned with articles which are required to have surfaces, or part thereof, which are resistant to erosion or abrasion.

Articles such as steam turbine blades are subjected in use to erosion of the blade surface by water droplets in the steam and one of the problems associated with the operation of steam turbines is the rate of erosion of the metal forming the blades.

According to this invention there is provided an article formed from titanium or a titanium-base alloy, at least part of its surface being more resistant to erosion by water droplets in steam than the remainder, if any, of the surface and consisting of a eutectiferous titanium-base alloy.

According to a feature of the invention the eutectiferous titanium alloy may consist of titanium with one or more of the alloying elements nickel, manganese, silicon, cobalt.

According to another feature of the invention the eutectiferous titanium alloy may consist of titanium with nickel and copper and, optionally, one or more of the alloying elements manganese, cobalt and silicon.

In the description which follows the components of the alloys are expressed in weight percent.

Alloys containing the ternary eutectic of titanium, nickel and copper are particularly useful for producing articles in accordance with the invention, and a suitable range of eutectiferous alloys is as follows:

Titanium and unavoidable impurities remainder.

Binary eutectiferous titanium alloys can also be used and such alloys which have conveniently low meling points are as follows:

Titanium with 20% to 35% nickel, Titanium with 35 to 45% manganese, Titanium with 20% to 32% cobalt and Titanium with 6% to 10% silicon.

Other alloys which are suitable include ternary and quaternary alloys with the above-mentioned elements in which a eutectic is present, the compositions being so se lected that the melting point is preferably below 1300 C.

A convenient manner of producing an article in accordance with the invention is to coat the surface of the titanium or titanium-base alloy where required by deposition of the eutectiferous titanium-base alloy by means of an inert gas-shielded arc-welding process, e.g. by the Argonarc process.

Surfaces treated in this manner are mechanically hard and have good resistance to erosion and abrasion, particularly in the case of erosion by water droplets in steam.

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The eutectiferous alloys are preferably at or near the eutectic composition since it is desirable that the melting point of the coating alloy should be well below that of the titanium or titanium-base article being coated in order to avoid undue dilution of the coating alloy by pick-up of titanium from the article.

The hardness of the coating of articles in accordance with the invention is such that these articles are suitable for applications in which abrasive conditions are encountered.

Whilst Vickers diamond pyramid hardnesses in the range 500-600 are achieved, the coating has reasonable resistance to spalling and chipping. Articles coated with titanium28% nickel, 10% copper, titanium-8.5% silicon and titanium-30% cobalt respectively withstand, without cracking, some deformation by hammering, the titanium-nickel-copper and titanium-silicon alloys having rather better resistance to cracking than the titaniumcobalt alloy which is the hardest of the three alloys.

Deposition of the eutectiferous alloy on the required surfaces of the article is carried out by a normal inert gas-shielded arc-welding process. The surface of the article should be freed from scale before performing the welding operation and descaling may be effected by immersion in a sodium hydride bath or an acid pickling bath. An adequate thickness of a eutectiferous alloy is deposited on the required surface and excess coating is subsequently ground off. Some allowance for the thickness of the coating may be necessary when the dimensions of the finished article are important.

By way of example, an article in accordance with the invention in the form of a steam turbine blade made from a titanium-base alloy is coated on the blade surfaces with a eutectiferous alloy by deposition of a titanium-28% nickel, 10% copper alloy by the Argonarc inert gasshielded arc-welding process and the blade is subsequently reduced to its final dimensions by grinding the coating. Such a turbine blade has a very high resistance to erosion by water droplets in the steam.

It will be appreciated that, although the invention is particularly applicable to articles such as turbine blades which are liable to erosion by water droplets in steam, articles in accordance with the invention may be employed for other purposes, e.g. where it is desirable to take advantage of the mechanical hardness of the surface.

We claim:

1. A steam turbine blade comprising: a base material selected from the group consisting of titanium and a titanium-base alloy, at least part of said turbine blade being more resistant to erosion by water droplets in high-velocity steam than any remaining part, said part consisting of an exterior coating on said base material, said coating having a lower melting point than said base material and consisting essentially of, by weight, 35 to 45% manganese with the balance being titanium and unavoidable impurities.

2. A steam turbine blade comprising: a base material selected from the group consisting of titanium and a titanium-base alloy, at least part of said turbine blade being more resistant to erosion by water droplets in high-velocity steam than any remaining part, said part consisting of an exterior coating on said base material, said coating having a lower melting point than said base material and consisting essentially of, by weight, 20% to 32% cobalt with the balance being titanium and unavoidable impurities.

3. A steam turbine blade comprising: a base material selected from the group consisting of titanium and a titanium-base alloy, at least part of said turbine blade being more resistant to erosion by water droplets in highvelocity steam than any remaining part, said part consisting of an exterior coating on said base material, said coating having a lower melting point than said base material and consisting essentially of, by weight, 6% to 10% silicon with the balance being titanium and unavoid able impurities. v

4. A steam turbineblade comprising: a base material selected from the group consisting of titanium and a titanium-base alloy, at least part of said turbine blade being more resistant to erosion by water droplets in highvelocity steam than any remaining part, said part consisting of an exterior coating on said base material, said coating having a lower melting point than said base material and consisting essentially of, by Weight, 28% nickel, 10% copper with the balance being titanium and unavoidable impurities.

References Cited in the file of this patent UNITED STATES PATENTS 2,570,248 Kelley Oct. 9, i951 4 2,576,793 Jordan NOV. 27, 1951 2,822,269 Long Feb. 4, 1958 2,847,302 Long Aug. 12, 1958 2,858,600 Vigor Nov. 4, 1958 2,900,715 Milnes Aug. .25, 1959 2,906,008 Boegehold Sept. 29, 1959 2,940,163 Davies June 14, 1960 OTHER REFERENCES Brazing Titanium to Titanium and to Mild and Stainless Steel, published December 1953, Wright Air Development Center, Wright-Patterson Air Force Base,

Ohio.

WADC Technical Report 52-313, part 2. 

1. A STREAM TURBINE BLADE COMPRISING: A BASE MATERIAL SELECTED FROM THE GROUP CONSISTING OF TITANIUM AND A TITANIUM-BASE ALLY, AT LEAST PART OF SAID TURBINE BLADE BEING MORE RESISTANT TO EROSION BY WATER DROPLETS IN HIGH-VELOCITY STEAM THAN ANY REMAINING PART, SAID PART CONSISTING OF AN EXTERIOR COATING ON SAID BASE MATERIAL, SAID COATING HAVING A LOWER MELTING POINT THAN SAID BASE MATERIAL, AND CONSISTING ESSENTIALLY OF, BY WEIGHT, 35% TO 54% MANGANESE WITH THE BALANCE BEING TITANIUM AND UNAVOIDABLE IMPURITIES. 